Force, Energy & Communication Lesson 13 & 14 WAVES.
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Transcript of Force, Energy & Communication Lesson 13 & 14 WAVES.
Force, Energy & Communication
Lesson 13 & 14
WAVES
Lesson objectives
Re-establish that all sound is caused by vibrations (waves)
Revise the links between pitch and wavelength; volume and amplitude.
Know a method for calculating the speed of sound
Learn the basic wave equation Measure the critical angle for a glass block
WAVES – the basics
Turn to p 158 of PHYSICS text book
WAVES – the basics
Waves vibrate in a regular fashion.
WAVES – the basics
All sound waves are caused by vibrations.
WAVES – the basics
Waves can transfer energy or information from one place to another.
WAVES – the basics
While the wave may transfer information or energy, it does not transfer matter.
WAVES – the basics
Nearly all the information we transfer is done by waves e.g. sound, radio, mobile phones, tv, etc
Measuring the speed of sound using the echo method
Measuring the speed of sound using the echo method
Speed = distance / time
Measuring the speed of sound using the echo method
Expt. no. Distance from wall (m)
No. of claps
Total distance travelled
Time (s) Speed of sound (m/s)
1 49 10
2 49 10
3 49 10
4 49 10
Measuring the speed of sound using the echo method
Expt. no. Distance from wall (m)
No. of claps
Total distance travelled (m)
Time (s) Speed of sound (m/s)
1 49 10 980 3.62
2 49 10 980 3.31
3 49 10 980 4.01
4 49 10 980 3.54
Measuring the speed of sound using the echo method Text book value for the speed of sound
through air is…..
Measuring the speed of sound using the echo method Text book value for the speed of sound
through air is…..330 m / s
The Wave Equation
A formula you are expected to KNOW!!
The Wave Equation
Turn to page 171 in the text book.
The Wave Equation
The wavelength ( )of a wave depends on two things:
1 the frequency of the wave
2 the speed of the wave
The Wave Equation
This can be expressed by the wave equation
The Wave Equation
This can be expressed by the wave equation
speed (m/s) = frequency (Hz) X wavelength (m)
The Wave Equation
This can be expressed by the wave equation
speed (m/s) = frequency (Hz) X wavelength (m)
N.B. frequency is measured in Hertz (or kilohertz). Hertz is another way of saying the number of waves in a second. E.g. 30 Hz = 30 waves every second
The Wave Equation
Copy out the example calculation off p171
Total Internal Reflection
Refraction happens when light is coming out of something dense like glass or water.
If the angle of the light is shallow enough, the light ray won’t come out at all but reflects back into the dense substance.
This is called total internal reflection because all the light reflects back in.
The angle over which total internal reflection occurs is called the critical angle.
The Wave Equation
Measuring the critical angle
Follow the instructions on your experiment sheet.
HOMEWORK
Complete all questions on the sheet on “Sound waves”.
Due in next Thursday